<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        *{
            margin: 0;
            padding: 0;
        }
        html body{
            height: 100%;
            width: 100%;
        }
        .box{
            width: 100%;
            height: 100%;
            background-color: pink;
            display: flex;
            /* flex-direction: row; */
            /* justify-self: center;
            align-self: center; */
        }
        .box1{
            width: 100px;
            height: 100%;
            background-color: yellow;
            
            
        }
        .box2{
            flex: 1;
        }

        .one{
            width: 0;
            height: 0;
            /* border: 0 20px transparent; */
            border-left: 10px solid transparent;
            border-right: 10px soild transparent;
            border-top: 20px solid pink;

        }
    </style>
</head>
<body>
    <div class="box">
        <div class="box1">1</div>
        <div class="box2">2</div>
    </div>

    <div class="one"></div>
</body>
</html>